The continuing goal of this project is to examine the interrelationship of cellular membranes in the intracellular transport and discharge of secretory proteins in the pancreatic exocrine cell. Specific topics to be studied include the following: 1) The properties of receptors for peptide secretagogues such as the octapeptide of pancreozymin will be examined on exocrine cells with the aim of determining a) the topographic distribution of receptor sites on the structurally polarized plasmalemma of the cell using peptide hormone derivatives visible by conventional and scanning electron microscopy and b) the biochemical properties of receptor sites covalently tagged with radioactively labeled photoaffinity probes; 2) We intend to determine, using fluorescent tagged hormones and hormone probes for electron microscopy, if secretagogue receptors are mobile in the plane of the membrane and whether induced redistribution affects cell function (exocytosis); 3) An examination of the factors regulating membrane -membrane recognition and fusion during exocytosis will be undertaken. Specifically, we will determine whether or not phosphorylation of secretory granule membrane proteins and/or those of the apical plasmalemma by cGMP dependent protein kinase(s) are key events in exocytosis; 4) The postulate that secretory granule membranes are cycled into the cell for reutilization following exocytosis will be put to direct test using morphologic (e.g., lectin - ferritin conjugates) probes and radiochemical tags for secretory granule membranes; 5) Finally, an investigation into the ontogeny of secretagogue receptors on developing pancreatic rudiments will continue with the aim of determining sites of receptor synthesis and assembly into the plasmalemma as a function of developmental age.